Clearing compositions for rapid processing of photographic film



United States Patent ABSTRACT OF THE DISCLOSURE A process for the preparation of positive photographic prints, free of blotchiness and mottle; from moist negatives using as a clearing composition, a thiocyanate agent and a salt of a polyvalent cation such as zinc, cadmium or tin and saturated aliphatic monocarboxylic or dicarboxylic anion.

This invention relates in general to photography and in particular to improved clearing-hardening compositions for the post-development treatment of exposed photographic film.

The advent of high speed rapid processing developing apparatus in the photographic industry wherein each of the operations associated with the post-exposure processing of an image bearing photographic film, e.g., silver halide emulsion, is carried out continuously and automatically, has of course led to significant reductions in processing time specifications as well as a decrease in overall production cost due to increased product throughput. In the main, rapid processing techniques depart from the more conventional procedures in the utilization of elevated temperatures, high-energy treating baths, etc., in order to accelerate the chemical reactions involved whether peculiar to the development and/or fixing operations. Resort to the use of such relatively severe conditions for the processing of photographic film has quite naturally imposed special demands upon the processor, since the formulations employed for each of the treating baths must be adjusted within the limitations of the particular film being treated in order to assure the attainment of optimum results. Thus, the acceleration of developer potential, for example, must not be at the expense of an increase in the fog characteristic of the film being treated. As a consequence, the art has provided a wide variety of additives for incorporation into one or more of the processing baths which purportedly function to augment and/or suppress certain and predetermined characteristics of the film material being treated, e.g., antifoggants, to reduce fog level within tolerable limits, wetting agents to promote faster and more uniform contacting of the processing solution with the emulsion strata of the film material, development accelerators, stabilizers and the like. In general, it is conceded that the film processing industry has the means at its disposal to formulate treating baths specifically adapted for the particular sensitometry problem which might be posed by a given film material.

Further attempts to decrease the time required for processing of exposed photographic film have been directed at the elimination of one or more of the washing and drying steps. Thus, it is known that the individual actions of separate processing baths can be effected by a single solution, e.g., developer-fixer compositions, fixerhardener compositions, etc. to realize substantial savings. In this manner, the advantages realized accrue not only from the fact that one phase of the processing is eliminated as Well as any intermediate washing and drying operations, but further, from the standpoint of reduced 3,525,567 Patented Aug. 25, 1970 handling as well. Despite the meritorious contributions to the art in this regard, the problem of providing additional manipulative techniques directed toward further reductions in the time required for complete film processing continues to challenge the practitioners of high "speed processing of silver halide photographic materials.-

The processing cycle typically characteristic fof the high speed methods currently used involves the successive operations of developing usually employing a high-energy hydroquinone developer compositioiii; fixing or clearing; and rinsing and/or dehydration in anf'alcohol wash, each of such operations usually being elfected at elevated temperatures, e.g., C. and higher. The moistfixed negative thus obtained must then be dried and possibly subjected to further washing operations prior to the preparation of a positive print therefrom. It has long been recognized that considerable savings both} in time and costs could be realized if the moist-fixed'gnegative obtained from the processing machine could be employed directly, i.e., without further washing, drying "or other treatment, to produce the desired print. However, prior attempts to do so have been unsuccessful since invariably, the moist negative would exhibit an intolerable degree of tack and, consequently, would adhere tenaciously to the film or paper print material thereby making clear separation extremely difficult. Furthermore, even in those instances wherein separation could be effected without substantial mutilation of the negative and/ or positive copy materials, it was found almost without exception, that the print obtained was heavily blotched, mottled or otherwise impaired. Upon close scrutiny, it was found that developable silver had been transferred from the negative onto the print which, of course, led to severe degradation of whites in the print obtained or fog in clear areas of a film print. Despite the considerable industrial efIort expended in an effort to overcome such drawbacks, the remedial techniques thus far evolved have failed to provide the requisite degree of improvement. Consequently, according to the current state of technology, the direct utilization of the moist negative obtained in rapid processing techniques is, in general, considered completely unfeasible for most commercial purposes.

Thus, a primary object of the present invention resides in the provision of a high-speed method for the production of photographic prints based upon the direct utilization of moist-fixed negatives for preparation of positive prints therefrom wherein the above and related disadvantages are eliminated or at least mitigated to a substantial extent.

Another object of the present invention resides in the provision of a high-speed photographic reproduction process wherein the positive print produced directly from a moist-fixed negative is substantially devoid of blotchiness, mottle and the like.

A further object of the present invention resides in the provision of photographic treating solutions particularly adapted for use in rapid-processing techniques.

Other and related objects of the present invention will appear hereinafter as the description thereof proceeds.

The above and related objects are accomplished in accordance with the present invention by the addition to the clearing solution employed in the treatment of the exposed photographic film of a compound comprising a salt of a polyvalent metal which is soluble in water or in a solvent which is substantially miscible with water. Suitable solvents include the lower aliphatic alcohols, e.g., methanol, ethanol, propanol and isopropanol; acetone and dioxane.

Without intending to be bound by any theory in explanation of the synergistic improvements made possible by the present invention, it has been determined that the silver thiocyanate complex formed in the negative as a result of the standardly used thiocyanate fixing operation diffuses or otherwise transfers to the print material during contact. The residues thus deposited manifest themselves in the form of imperfections in the final print, e.g., mottled, blotchiness, streakiness, etc. The latter result is, of course, particularly evident in the non-image, i.e., white or clear areas, of the print material. However, the cation present in the polyvalent metal salts contemplated by the present invention apparently function to bind up any thiocyanate ion present in the form of a colorless complex, thus efiectively inhibiting transfer of the reducible silver complex ion or its dissociation products. In this manner, spurious deposits leading to reproduction imperfections are completely avoided.

Soluble polyvalent metal salts suitable for use herein may be selected from a relatively wide variety of materials so long as they meet the following requirements: 1) be soluble in water or a water-miscible solvent; (2) contain a polyvalent metal cation; (3) the cation be capable of forming a colorless complex with thiocyanate ion under the conditions of treatment; and (4) the anion of the polyvalent metal salt must be chosen in such a manner that it does not form with the silver ion a water-soluble complex. Particularly beneficial results are found to obtain with water-soluble compounds comprising salts of the polyvalent metal with saturated, monocarboxylic and dicarboxylic acids preferably containing from 1 to 8 carbon atoms. The cations include zinc, cadmium and tin ions. Suitable anions derived from monocarboxylic and dicarboxylic acids include the formates, acetates, propionates, malates, malonates, maleates, succinates, tartrates, glutarates, glycinates, alaninates, glyoxylates, pyruvates, glycolates, benzoates, salicylates and the like. It will be noted that the above anions are derived not only from unsubstituted acids but also from those which carry an amino keto or hydroxy substituent. As particular examples of such compounds, there may be mentioned without necessary limitation the following:

cadmium acetate zinc benzoate cadmium benzoate zinc butyrate cadmium formate zinc caproate cadmium fumarate zinc formate cadmium lactate zinc lacate cadmium salicylate zinc salicylate stannous tartrate zinc valerate zinc acetate The concentration of polyvalent metal salts selected will depend on several considerations, the principal and controlling factor being the concentration of thiocyanate employed in the clearing hardener bath. Quite obviously, the concentration selected will be sufficient to complex the entire amount of thiocyanate present in the moist cleared film. For purposes of assuring such a result, it may be advisable in a particular circumstance to employ the salt in excess amounts. Beyond this requirement, little in the way of critically attaches to the amount selected. In general, optimum results can be obtained by the use of the polyvalent metal salt in concentrations ranging from about 25 grams to about 100 grams per liter of clearing hardener solution with a range of 30 grams to 70 grams being particularly preferred.

One of the truly valuable aspects of the present invention relates to the fact that its practice makes possible the use of materially higher concentrations of thiocyanate, e.g., the alkali metal thiocyanate, ammonium thiocyanate, etc., in the fixer solution. In this connection it has been determined that thiocyanate concentrations ranging from 150 grams to 400 grams per liter of fixer solution may be readily employed to advantage. This consideration is of paramount importance in rapid processing systems since the thiocyanate concentration determines the rate of fixation. Consequently, reductions in processing time to an extent heretofore considered unattainable are made possible by the use of thiocyanate in amount substantially in excess of those employed in the more standard types of fixer solutions. Previously, the concentration of thiocyanate was necessarily limited to the lower ranges in order to avoid burdensome and time consuming post-fixing washing operations.

Apart from the thiocyanate and polyvalent metal salt, the remaining components of the fixer composition are conventional, being well known in the photographic art. Thus, hardening agents such as the alums may be added to retard any tendency of the photographic emulsion to swell and/or soften due to continued and protracted immersion in the treating solutions. However, it will be understood that such ingredients are optional elements only and may be omitted without deleterious effects on the photographic emulsion being treated. In any event, suitable results are obtained with potassium alum, sodium alum, ammonium alum, etc.

In order to promote a better understanding of the present invention, the following specific embodiments thereof are presented but it is to be understood that such embodiments are given for purposes of illustration only and are in no way to be considered as being limitative of the present invention.

EXAMPLE I-A An imagewise exposed commercially available silver halide photographic fihn was developed in a high-energy hydroquinone developer to give a black and White image and then treated with a clearing solution of the following composition:

Water-460 ml.

Potassium alum-46.5 g.

Sodium acetate10 g.

Sodium bisulfite-S g.

Sodium thiocyanate (50% aqueous solution in water) The film was then rinsed. The moist negative was then placed in contact with a strip of printing paper in a contact printing frame. The sandwich was exposed to light for a short period of time to form a latent image. After subsequent conventional processing, including developing, fixing and washing, the paper strip showed severe silver fogging and mottling. The gelatin emulsion coating of the processed film coating was tacky; and it was very difficult to separate the paper from the film.

EXAMPLE I-B Example I-A was repeated except that the alum was omitted from the clearing solution and replaced by 50 grams of zinc acetate. The positive strip produced from the moist negative showed little or no mottling or blotching. Clean white areas developed comparable to those on a normally exposed and processed strip. The moist surface of the freshly processed film was not tacky or sticky.

EXAMPLES II-VIII Results similar to those described above are obtained when the processes exemplified are repeated but employing in lieu of zinc acetate in equivalent amounts Within the range specified the following materials:

zinc formate zinc o-lactate zinc salicylate cadmium acetate cadmium maleate stannous tartrate zinc butyrate 5 6 What is claimed is: cyanate is sodium thiocyanate and the salt is zinc acetate. 1. A process for the preparation of positive photo- 3. A process as defined in claim 1 wherein the salt is graphic prints from moist negatives which comprises present in amounts ranging from 25 grams to 100 grams (a) immersing the developed negative in a clearing per liter of clearing bath.

bath comprising a thiocyanate fixing and clearing 5 agent and a salt soluble in water and water-miscible References Cited solvent, said salt containing a cation, capable of form- UNITED STATES PATENTS ing a colorless complex with thiocyanate ion, selected from the group consisting of zinc, cadmium and tin 3239340 3/1966 Nasa et a1 96-61 and an anion selected from the group consisting of 10 3243296 3/1966 Nasa et a1 96*61 saturated aliphatic monocarboxylic acid and satu- 3282694 11/1966 i k 96 61 rated aliphatic dicarboxylic acid containing from 1-6 3326684 6/1967 Nlshlo 96 61 carbon atoms; 3,300,306 1/1967 Sevens 9666 (h) rinsing and squeegeeing the fixed negative; FOREIGN PATENTS (c) placing the moist negative in contact with a strip 15 379 281 8/1964 Switzerland of printing paper; (d) exposing the printing paper to light through the NORMAN TORCHIN, Primary Examiner negative and (e) developing and fixing the exposed printing paper KELLEY, Asslstant Exammel whereby a print free from blotchiness and mottle is 20 U S Cl X R prepared. 96 61 2. A process as defined in claim 1 wherein the thio- 

